LAUNCHING DATA FOR A BATTLESHIP. 97 



the ways, but is graduated for horizontal travel. The marks on the vessel are 

 made as verniers, so as to read to one-tenth of a foot. They are attached to the 

 vessel so as to stand parallel to the scale, and to project just above the scale in the 

 picture. The marks or verniers on the ship are placed so that before one leaves 

 the scale the next one comes on; each is laid out for the position it will occupy on 

 the ship, and is expanded over the size of a vernier at the distance of the scale, in 

 the proportion that its distance from the camera when crossing the axis of view 

 is to the distance of the scale where it crosses the axis. The clock is placed so as 

 to show in the center of the picture, just under the scale. A vernier is added to 

 the long hand so that with sufficient magnification the clock reads minutes, seconds, 

 and tenths of a second. It is also advisable to add two vertical scales for use in 

 determining the trim, the position when the vessel lifts, and for measuring the 

 height of the waterline. 



It is not suggested that moving-picture data is desirable for all launches ; the 

 curves, Plate 38, show that stop-watch observations, carefully made, give reliable 

 information. It is to be noted, however, that dimensions and launching weights 

 change ; practices, precautions and other launching conditions change ; the kind and 

 quality of materials that must be used change; and it is advisable that launchings 

 be rigidly investigated from time to time and that accurate observations and records 

 be made. Photographic methods offer advantages to that end. 



Parts of the launching operation deserving further investigation are the start, 

 and the waterline just before lifting. The latter can be studied from the record 

 of one or two moving-picture cameras placed to give a clear view of the water- 

 line, and of vertical gauges and scales. Information as to actual start and initial 

 friction would be obtained from a moving-picture record taken by a camera close to 

 the forward end of the ways, to give a large-sized view. A long reading pointer 

 could be attached to the ways to magnify the movements for the first inch of travel. 



The over-run before pivoting is influenced by surrounding obstructions that 

 interfere with the free flow of water to the ways, and by the proportion of the 

 prism-section of the vessel to the prism-section of the water in the slip, as well 

 as by the velocity. A mask used across the stern for checking tends to increase 

 the over-run, and it may happen, due to the various causes, that the vessel not only 

 over-runs the estimated pivoting point, but also has a tipping moment in excess of 

 that estimated for static conditions. 



U. S. S. Oklahoma. 



LAUNCHING DATA. 



Type of vessel Battleship, First Line 



Builders New York Shipbuilding Company, Camden, N. J. 



Date of launch March 23, 1914 



